1. Field of the Invention
The present invention relates to an anti-reaction valve device capable of inhibiting a reaction of a hydraulically powered actuator configured to drive an element, and a control unit and a hydraulically powered system comprising the anti-reaction valve device.
2. Description of the Related Art
FIG. 12 is a cross-sectional view showing the conventional anti-reaction device 1 disclosed in, for example, Japanese Patent No. 3164469. FIG. 13 is a view showing a hydraulically powered system 3 comprising anti-reaction valve devices 1 and 2. As used herein, the term “rotation” means an angular displacement with an angle less than 360 degrees. The hydraulically powered system 3 is configured to cause, for example, a turn table of a construction machine to be driven to rotate. The hydraulically powered system 3 is equipped with a hydraulically powered motor 4 connected to the turn table (not shown). Pipes 7 and 8 are connected to inlet and outlet ports 5 and 6 of the hydraulically powered motor 4, respectively. Hydraulic oil is supplied to the hydraulically powered motor 4 by a hydraulic pump 10 through the pipe 7 or the pipe 8 via a directional control valve 9 to cause the hydraulically powered motor 4 to rotate, thereby causing the turn table to be driven to rotate.
When the hydraulically powered motor 4 stops driving the turn table, it tends to react. If supply of the hydraulic oil is stopped to cause the hydraulically powered motor 4 to stop driving the turn table in the state in which the hydraulically powered motor 4 is driving the turn table, then the hydraulically powered motor 4 tends to continue rotation due to inertia. As a result, a pressure of the hydraulic oil on the supply side becomes lower than the pressure of the hydraulic oil under the state in which the motor 4 is driving, and a pressure of the hydraulic oil on the return side becomes higher than the pressure of the hydraulic fluid under the state in which the hydraulically powered motor 4 is driving. This causes the hydraulically powered motor 4 to rotate in an opposite direction to the rotation to drive the turn table. The hydraulically powered motor 4 counterrotates repeatedly, which phenomenon is called the reaction.
In order to inhibit such a reaction, the hydraulically powered system 3 is equipped with two anti-reaction valve devices 1 and 2 between the pipes 7 and 8 such that directional relationship of connection of primary ports 11 and secondary ports 12 between the pipes 7 and 8 may be reversed between the anti-reaction valve devices 1 and 2, i.e., the hydraulic oil flows within the primary ports 11 in a reverse direction and flows within the secondary ports 12 in a reverse direction between the anti-reaction valve devices 1 and 2. The anti-reaction valve devices 1 and 2 have the same construction, and therefore, a schematic construction of the anti-reaction valve device 1 will be described with reference to FIG. 12.
Referring to FIG. 12, the anti-reaction valve device 1 comprises a casing 13 having the primary port 11 and the secondary port 12, a plunger 15 having a cylinder bore 14, a sheet member 16, a piston 17 slidably fitted in the cylinder bore 14, a first spring 18 configured to press the plunger 15 in the opposite direction to the sheet member 16, and a second spring 19 configured to press the sheet member 16 toward the plunger 15. The casing 13 has a plunger storage bore 20 and a sheet member storage bore 21, and has a valve chamber 24 at an intermediate portion of the plunger storage bore 20 and the sheet member storage bore 21 with the valve chamber 24 interposed between land portions 22 and 23. The plunger 15 and the sheet member 16 are sidably fitted to the land portions 22 and 23 and are configured to move into contact with or away from each other within the valve chamber 24.
The plunger 15 is provided with a small bore 25 extending in an axial direction of the plunger 15 and configured to open in the cylinder bore 14. The sheet member 16 is provided with an inner bore 26 extending in an axial direction of the sheet member 16 and configured to open in the primary port 11. Within the sheet member storage bore 21, a damping pressure chamber 28 is formed to communicate with the primary port 11 through an orifice 27, and the plunger storage bore 20 communicates with the secondary port 12.
Spring forces (loads) of the first and second springs 18 and 19 are set so that when a primary pressure of the hydraulic oil on the primary port 11 side is higher than a secondary pressure of the hydraulic oil on the secondary port 12 side, and a difference pressure obtained by subtracting the secondary pressure from the primary pressure rapidly decreases from not less than a first set pressure value to less than the first set pressure value, the plunger 15 and the sheet member 16 move away from each other, while when the secondary pressure is higher than the primary pressure, and a difference pressure obtained by subtracting the primary pressure from the secondary pressure rapidly decreases from not less than a second set pressure value to less than the second set pressure value, the plunger 15 and the sheet member 16 move away from each other. And, a steel ball 29 is provided between the plunger 15 and the sheet member 16 and configured to close the inner bore 26 when the secondary pressure is higher than the primary pressure.
The anti-reaction valve devices 1 and 2 thus constructed allow the hydraulic oil to move between the pipes 7 and 8 to inhibit counterrotation of the hydraulically powered motor 4, when the hydraulically powered motor 4 stops driving. This makes it possible to inhibit the reaction of the hydraulically powered motor 4.
As described above, in the conventional anti-reaction valve devices 1 and 2, the steel ball 29 is provided between the plunger 15 and the sheet member 16 to close the inner bore 26 when the secondary pressure is higher than the primary pressure. In the anti-reaction valve device 1 having a structure for inhibiting flow of the hydraulic oil from the secondary port 12 to the primary port 11 by using the steel ball 29 interposed between the plunger 15 and the sheet member 16, if the hydraulic oil in the secondary port 12 leaks into a gap between the plunger 15 and the sheet member 16 directly or through a gap between the plunger 15 and the piston 17 under the condition in which the secondary pressure is higher than the primary pressure, the sheet member 16 and the steel ball 29 are pushed to be moved together away from the plunger 15, so that the plunger 15 and the sheet member 16 become distant from each other. If such an event takes place, the anti-reaction valve devices 1 and 2 may malfunction, i.e., open when the these devices 1 and 2 should not open to inhibit the reaction.